1. Field of the Invention
The present general inventive concept relates to scalable audio data decoding, and more particularly, to a method and device to provide arithmetic decoding of scalable bit sliced arithmetic coded (BSAC) audio data.
2. Description of the Related Art
Audio lossless encoding is frequently used for audio broadcasting or archiving. Lossless audio encoding is generally performed using an entropy coder using a time/frequency transformation or linear prediction.
When scalability is used in bitstream re-parsing, a bitstream corresponding to one frame may be truncated at any location at a server level and transmitted to a decoder. Accordingly, it is difficult to decode scalable bitstreams which have been truncated.
FIG. 1 is a flowchart illustrating a conventional arithmetic decoding method. First, initialization is performed (operation 100), and then a search is performed for a symbol to be decoded (operation 110). A probability of the symbol is calculated using a context (operation 120), and arithmetic decoding is performed (operation 130). Then, it is checked whether the symbol is the end of a bitstream (operation 140). When the symbol is determined not to be the end of the bitstream, the aforementioned operations are repeated to search for the symbol to be decoded, and when the symbol is determined to be the end of the bitstream, decoding is completed. In the arithmetic decoding, an entire symbol to be decoded or a predetermined bitstream length should be known, or a decoder is provided with information on when to terminate the decoding by inserting a specific termination code. However, as illustrated in FIG. 2, when the bitstream is truncated, since the information is truncated, the symbol or the termination code cannot be found and the decoder does not know when to terminate the decoding. Thus, undesired data may be decoded.
Bit Sliced Arithmetic Coding (BSAC) is a popular Moving Picture Experts Group (MPEG)-4 standard for scalable audio coding which is used widely in digital audio (e.g., digital audio streaming or audio on demand), internet streaming, and Digital Media Broadcasting (DMB). MPEG-4 BSAC offers good sound quality at bit rates between 40 kbps to 64 kbps, but allows for degradation at lower bit rates. In MPEG-4 BSAC, the above truncation problem is even more severe since scalability with units of 1 kbps/ch (i.e., 1 kbps/mono or 2 kbps/stereo) is provided using side information. This results in poor decoding efficiency, especially at lower bit rates.